Fix Issue 17452 - Undefined references in std.container.array

[wilzbach]

As long as DIP82 isn't implemented, it's a pretty bad idea to use unittest blocks within a templated aggregate.
This is one of the few small things that broke Vibe.d and the Dlang-Tour with dmd-nightly ...

CC @ZombineDev

The linker error can be observed starting with #5295

[dlang-bot]

Fix	Bugzilla	Description
✓	17452	Undefined references in std.container.array

[JackStouffer]

This has the added benefit of reducing compile times, yeah?

[wilzbach]

This has the added benefit of reducing compile times, yeah?

Yes, but I think this is marginal compared to all the crazy CTFE-stuff that we do in other modules ;-)

All in all I do have the opinion that such errors should be detected/warned by a compiler, but this way seemed a lot easier to go than reducing entire Vibe.d again.

[PetarKirov]

Thanks for tracking down linker errors @wilzbach!

If those were documented unittests, I would have suggested​ using the static if (doDocUnittests) trick, but since that's not the case, moving them outside is a better solution, so LGTM as well. Actually I don't know if that trick would have fixed the problem. It looks #5295 exposed a compiler bug, since there's no apparent reason for the linker errors.